This application claims priority to Japanese Patent Application No. 2001-036231 filed on Feb. 13, 2001. This application is also related to U.S. application Ser. No. 09/987,027 filed on Nov. 13, 2001. The entire contents of both applications are herein incorporated by reference.
1. Field of the Invention
The present invention relates to a powder pump to be used in an image forming apparatus, such as a copying machine, a facsimile, a printer, and other similar devices, and more particularly to a powder pump that can effectively convey a powder.
2. Discussion of the Background
A powder pump that conveys various types of powders is commonly known. For example, in an image forming apparatus such as a copying machine, a facsimile, a printer, and a multifunctional image forming apparatus having at least two of the above-described functions, a powder pump is used to convey toner or a two-component developer including toner and a carrier (for example, in Japanese Patent Laid-Open Publication No. 11-84873). Generally, such a powder pump is referred to as a uniaxial eccentricity screw pump or Moineau pump.
The above-described powder pump is configured such that a cavity, which is formed between an outer peripheral surface of a rotor and an inner peripheral surface of a through hole of a stator, moves according to a rotation of the rotor. Thus, a powder enclosed in the cavity is conveyed. Generally, the rotor is formed of a rigid member, such as metal or resin, and the stator is formed of a elastic material, such as rubber or soft resin, for example.
Hermeticity of the cavity is enhanced to increase a suction force of a powder pump so that an amount of a powder to be conveyed per unit of time is increased. An outer peripheral surface of a rotor (which is more rigid than the stator) is in press-contact with an inner peripheral surface of a through hole of a stator, which is formed of an elastic member. The press-contacting rotor elastically deforms the inner peripheral surface of the through hole of the stator, hereafter referred to as the deformation of the stator. In order to enhance the hermeticity of the cavity, the deformation of the stator is increased, thereby increasing the press-contacting force of the rotor portion and the stator portion around the cavity.
However, if the stator excessively deforms, problems such as increased rotor torque cause wear on the stator, and the temperature of the powder pump 1 is increased due to friction produced between the rotor and stator arises. Thus, if a powder conveyed by the powder pump is one that is easily influenced by heat, the powder may be adversely affected by an increase in the temperature of the powder pump. For example, if the powder is toner or a two-component developer having toner and a carrier, the toner tends to coagulate by the increase in the temperature of the powder pump.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel powder pump in which a powder is effectively conveyed while minimizing the above-described difficulties.
According to an example of present invention, the powder pump includes a stator having a through hole comprised of two spirally extended grooves and a rotor, which is rotatably provided to the through hole of the stator and is spirally extended such that a cavity to convey a powder is formed between an outer peripheral surface of the rotor and an inner peripheral surface of the through hole of the stator. The rotor is configured to convey the powder enclosed in the cavity while moving the cavity. The following equations illustrate a non-limiting embodiment of the present invention:
RAxe2x88x92SNxe2x89xa70.45
and RBxe2x88x92(SN+SX)/2xe2x89xa70.45,
or xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.16
or RAxe2x88x92SNxe2x89xa70.4, RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.12,
and xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.12,
or (4) RAxe2x88x92SNxe2x89xa70.5
and RBxe2x88x92(SN+SX)/2xe2x89xa70.5,
and xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.12,
or 0.9xe2x89xa6SN/2SRxe2x89xa60.95,
where a diameter of a cross section of the rotor, an outer diameter of the rotor, a minimum inner diameter of the through hole of the stator, a maximum inner diameter of the through hole, a radius of each groove of the through hole of the cross section of the stator are in millimeters and represented by RA, RB, SN, SX, and SR, respectively.